The present invention relates more particularly to a turbine wheel comprising:                a plurality of blades; and        a disk presenting an axis of rotation with the blades mounted at a periphery thereof, each of the blades having a head that is solid with a root that is itself engaged in a housing opening out to the periphery of the disk.        
It is well known that when turbine wheels are in operation, in particular within a turbine engine, they are subjected to large variations of vibratory excitation forces.
Under certain circumstances, those vibratory excitations can give rise to high levels of vibration that are harmful and that can lead to the turbine wheel breaking. If the vibratory excitation causes the turbine wheel to enter resonance, i.e. if the frequency of the vibratory excitation corresponds to the resonant frequency of the turbine wheel, and if the resonant deformation mode of the wheel is excitable by the vibratory excitation forces acting on the wheel, then the wheel will present vibration of very large amplitude, subjecting the material of the wheel to mechanical fatigue and in the extreme leading to its destruction.
One technical solution might be to reinforce the mechanical strength of the turbine wheel so that it can withstand vibration better.
Nevertheless, such a solution is not acceptable, in particular when the turbine wheel is for mounting in a turbomachine.
In the design of a turbomachine, the very stringent targets concerning the performance, the fuel consumption, or the mass of the turbomachine, the rotor inertia targets for enabling acceleration to be sufficient, and the targets of complying with reliability requirements or with regulations together impose multiple constraints on the design and sometimes reduce room for maneuver in terms of improving mechanical strength.
By way of example, the technical specifications include a design constraint that the blades must break before the disk breaks in the event of the turbine wheel spinning too fast, in order to limit the energy of any debris, to brake the rotor, and to protect the other elements of the drive train. This situation may occur, for example, in the event of a part of the drive train of the turbomachine breaking, such that a turbine wheel connected to the drive train is no longer subjected to an opposing rotary torque. Under such circumstances, it can be understood that the turbine wheel can then rotate at very high speed, the turbine then being said to be subjected to “overspeed”. To avoid the turbine wheel bursting or spinning even faster, which would severely damage the turbomachine, and in order to eliminate the rotary drive torque, the blades are dimensioned so that they break at a given speed of rotation that is slower than the speed at which the turbine wheel would break.
It can thus be understood that the design of a turbine wheel needs to satisfy contradictory targets and that a compromise needs to be found.
By way of example, in order to respond to a problem of vibratory resonance, it is already known to use dampers that are placed between the blades or between the blades and the disk. Nevertheless the use of dampers can be very expensive, since their effect can be verified only very late in the design process, by performing tests on engines. The problem of vibratory resonance remains undiminished if the dampers are not capable of shifting resonance to outside the operating range in which the vibratory excitation is harmful or if the dampers do not enable the amplitude of the vibration to be reduced sufficiently. The outer platforms of the blades or other damper systems may also perform an equivalent function by means of the contacts they establish between adjacent blades.